Arrived on site and was shown reach in freezer not keeping temp. Stated it rises up to 50 degrees then pulled down and has been maintaining since. Found some ice on evap coil. Deiced quickly as this ice wouldn't be defrosted by the heaters. Exposed condenser coil to find blanket of lint. Brushed clear and ensured good airflow. System was struggling due to lack of airflow through condenser. Watched system pull down after having doors open for several minutes. System went through defrost cycle then began to cool from 50 degrees to 0 in several minutes. All work is complete.